The present disclosure relates generally to systems and methods for use in radiotherapy treatment delivery. More particularly, the disclosure relates to systems and methods for real-time treatment margin adaptation during radiotherapy for moving tumors.
External beam radiation therapy is designed to selectively destroy tumor tissue by administering large, spatially-controlled doses of radiation to a subject. The “Rule of Thumb” for such procedures is that the dose delivered should be within ±5 percent of the planned dose and within ±5 mm of the planned position. The treatment process proceeds through a number of steps, beginning with a contoured dose prescription indicated by a radiation oncologist using a set of diagnostic images. A dosimetrist, with the aid of a treatment planning system (TPS), then determines the dose to be delivered from each of a set of beam geometries and incident angles. The TPS utilizes stored dosimetric information, which is typically obtained from measurements on phantoms, to deterministically calculate dose delivery. Once the treatment plan has been approved by the oncologist, the treatment regiment begins. Prior to radiation delivery, the subject is positioned as exactly as possible to match the position used for treatment planning. This includes the alignment of skin markers with room lasers and the acquisition of CT or x-ray images for registration with planning images using either intrinsic or extrinsic fiducial markers. Typically, kilovoltage (kV) imaging is performed using an on-board imaging device (OBI) or megavoltage (MV) imaging is performed using an electronic portal imaging device (EPID). Immobilization devices can also be used to further increase positioning accuracy and minimize movement during treatment. After proper measures are taken to ensure a subject accurately receives the planned treatment, the radiation dose is delivered, typically at a rate of approximately 400 to 600 cGy per minute.
During external beam radiotherapy, patient setup uncertainties, as well as intrafractional tumor motion, cause a blurring of the delivered dose distribution relative to the dose distribution simulated during treatment planning. A commonly implemented strategy to account for this effect in the treatment plan is to enlarge the treated volume by utilizing geometric safety margins. The margin size is estimated by evaluation of pre-treatment data (e.g., 4DCT) and/or population based data. However, this concept relies on assumptions regarding both setup uncertainties and tumor motion during treatment delivery. The tumor position may change during radiation delivery due to several factors, such as respiration, peristalysis, relaxation, and the like. Inaccurate estimations of either setup or tumor margin may lead to undesirable dose distributions, such as under-dosing the tumor or overdosing surrounding healthy tissue.
Various techniques have been developed over recent years to facilitate motion management for moving tumors, mainly with respect to respiration which can be responsible for large tumor motion amplitudes. Couch tracking and dynamic multi-leaf collimator tracking both have been shown to be viable options for “freezing” tumor motion with respect to the treatment beam.
However, previous feasibility studies have maintained static treatment margins, even when real-time information is available. It would therefore be desirable to have a system and method for accurately locating the target, and to adapt the treatment aperture based on real-time confidence in the localization. It would also be desirable to have a system and method that utilizes a technique that is applicable regardless of the chosen in-treatment imaging type (e.g., MRI, kV, MV, etc.) and motion mitigation technique, such as multi-leaf collimator (MLC) tracking, couch tracking, and the like.